Abstract

Greenhouse experiments were conducted to study the effects of glyphosate drift on plant growth and concentrations of mineral nutrients in leaves and seeds of non-glyphosate resistant soybean plants (Glycine max, L.). Glyphosate was sprayed on plant shoots at increasing rates between 0.06 and 1.2% of
the recommended application rate forweed control. In an experiment with 3-week-old plants, increasing application of glyphosate on shoots significantly reduced chlorophyll concentration of the young leaves and shoots dry weight, particularly the young parts of plants. Concentration of shikimate due to increasing glyphosate rates was nearly 2-fold for older leaves and 16-fold for younger leaves compared to the control plants without glyphosate spray. Among the mineral nutrients analyzed, the leaf concentrations
of potassium (K), phosphorus (P), copper (Cu) and zinc (Zn) were not affected, or even increased significantly
in case of P and Cu in young leaves by glyphosate, while the concentrations of calcium (Ca),
manganese (Mn) and magnesium (Mg) were reduced, particularly in young leaves. In the case of Fe, leaf
concentrations showed a tendency to be reduced by glyphosate. In the second experiment harvested at
the grain maturation, glyphosate application did not reduce the seed concentrations of nitrogen (N), K, P,
Zn and Cu. Even, at the highest application rate of glyphosate, seed concentrations of N, K, Zn and Cuwere
increased by glyphosate. By contrast, the seed concentrations of Ca, Mg, Fe and Mn were significantly
reduced by glyphosate. These results suggested that glyphosatemay interfere with uptake and retranslocation
of Ca, Mg, Fe and Mn, most probably by binding and thus immobilizing them. The decreases in
seed concentration of Fe, Mn, Ca and Mg by glyphosate are very specific, and may affect seed quality.